SINGAPORE: The National Environment Agency has clarified that the hail seen in Singapore on Tuesday was not due to cloud seeding over Indonesia.

Though winds can potentially bring clouds a distance downward, the agency said, it was unlikely the clouds could travel as far as the distance between Indonesia and Singapore.

The agency said hail forms in very intense thunderstorms clouds, particularly those with great vertical extent and large water droplets.
Thunderstorms occurred on Tuesday in the western parts of Singapore.

NEA said hail is quite rare in Singapore. The last reported hail storm was in 2009.

More afternoon thunderstorms are expected over the next few days.

However, because it is still unknown what the impact of the rain is on PM2.5 concentrations, the government's health advisory remains cautious.

The Ministry of Environment and Water Resources said studies have shown that rain is not so effective in washing away PM2.5 concentrations.

The authorities will be closely monitoring the situation to see if the rain has any positive impact on PM2.5 concentrations, and will change its health advisory accordingly.

The brief respite from the haze is expected to continue on Wednesday with the 24-hour PSI reading forecast to be in the moderate range of 51 to 100.

But as the PM2.5 concentrations are still in the unhealthy levels, the authorities said Singaporeans should remain cautious and minimise outdoor physical activity.

Separately, the Health Ministry said up to 515 GP clinics have come on board its special subsidy scheme for haze-related conditions.

SINGAPORE – The rain that had fallen over parts of Singapore this afternoon (June 25) is neither toxic nor acidic, said the National Environment Agency (NEA).

It is also not due to cloud-seeding in Indonesia, said the NEA’s metereologist Patricia Ee in today’s daily haze briefing. She said that rain clouds could not have crossed over from Indonesia as it is too far away.

After a dry spell lasting several days, rain fell in Singapore this afternoon, with reports of hailstones falling in western areas like Chua Chu Kang, Bukit Batok and Jurong East.

According to the NEA, this is the first time in five years hail has been reportedly seen in Singapore. On March 27, 2008, hailstones rained over the central part of Singapore.

Several social media users sent in pictures of the ice. Some wondered if the cloud seeding operation in Indonesia was the cause.

Hail, which comprises of irregular lumps of ice, forms in strong thunderstorm clouds, when supercooled water droplets freeze on contact with condensation nuclei.

While it is uncertain if haze causes hail, Ms Ee said that the intense thunder clouds this afternoon created the right conditions for hail to form. Any kind of particles, such as haze or dust, can cause condensation nuclei, which could then lead to ice formation.

In a Facebook post, Minister for Environment and Water Resources Vivian Balakrishnan said: “Heavy but short thunderstorm, especially in the western parts of Singapore brought some hailstones.”

“No, we did not do cloud seeding,” he added.

Earlier today, the NEA said moderate to heavy thundery showers with gusty wind were expected over southern, eastern and central areas of Singapore between 3.25pm and 4.25pm.

Meanwhile, a caller to the MediaCorp hotline, Mr Bai, said that about three trees had fallen along the PIE, near the Bukit Batok exit towards Changi, crashing into several cars during the rain.

The SCDF said it received calls near 3pm requesting for assistance. Rescue tools were used to release the trapped people in the cars and no injuries were reported. A fire engine, red rhino and ambulance were sent to the scene.

Hail rains down on western Singapore
Grace Chua Straits Times 26 Jun 13;

RESIDENTS in the west of Singapore scurried for cover yesterday as a rare hailstorm uprooted trees and disrupted traffic.

The phenomenon - which was last reported here in 2008 - may or may not be linked to haze, said the National Environment Agency (NEA) and weather experts.

But it is unlikely to have been triggered by cloud seeding in Indonesia to extinguish fires in Riau, they said, as the seeding took place hundreds of kilometres away, and hail is a local phenomenon.

"Hail is produced by sizeable cumulonimbus clouds located in very high altitude where temperature is very low," said atmosphere scientist Erwin Mulyana of Indonesia's Agency for the Assessment and Application of Technology. "Above Riau, the cumulonimbus clouds are thin and small, and are not at a high altitude."

Both the NEA and external experts did not rule out the possibility that fine haze particles in the air had helped to produce hail.

Weather researcher Matthias Roth, a National University of Singapore associate professor of geography, said haze particles could have acted as tiny nuclei for water to condense and freeze around. "But I cannot say for sure - cloud microphysics is a very complicated scientific field," he said.

Yesterday's storm was the first since the haze episode began last week, and was accompanied by heavy rain and powerful winds.

The NEA said there may be more afternoon thunderstorms in the next few days. It warned that while the rain may have washed coarse haze particles from the sky, it will take longer to wash out finer particles - like those smaller than 2.5 microns in size.

The NEA and experts said the rain was not toxic to people, though it may have contained haze particles. Water agency PUB has stepped up its water quality monitoring since last week.

Today, the 24-hour Pollutant Standards Index is expected to be moderate (51 to 100) until 6pm. But the health advisory is for unhealthy conditions, based on yesterday's 24-hour PM2.5 readings.

FREAK weather conditions, including hail, wreaked havoc in the western part of Singapore yesterday afternoon.

Several roads were blocked by uprooted trees, causing massive traffic jams during and after the heavy downpour. The exit to Jurong Town Hall road on the PIE, Bukit Batok Road, Toh Guan Road and Old Jurong Road were some roads that were affected.

Items such as bamboo poles and plastic chairs were sent flying by strong winds. And at least three cars were damaged by falling trees and branches.

Two of the cars - a Toyota Vios and a Toyota Camry - had been parked at a building's open-air carpark on Toh Guan East Road, just beside the Pan Island Expressway.

Ms Crystal Wong, the owner of the Vios, was shocked by the sight of a tree on top of her car as she walked towards it after work at about 5pm. Her car had to be towed away.

"I don't usually park here," said the 31-year-old project manager, who works in a neighbouring building, bemoaning her bad luck. "The lots at my office building were all occupied because I was slightly late today."

The Camry, which served as Lay Auto's company car, had its roof damaged by the uprooted tree. Staff had earlier moved five other cars from the carpark to the showroom when branches were swaying wildly in the rain.

The third car was damaged while parked at Bukit Batok West Avenue 2.

The weather also caused part of the ceiling in the Church of St Mary of the Angels on Bukit Batok East Ave 2 to come crashing down.

Retiree Ang Lam Toh, who was at a coffee shop in Bukit Batok West Avenue 4 at 3pm yesterday, said he saw ice pellets - as large as 50-cent coins - falling from the sky, accompanied by heavy rain and gusts of wind so strong that plastic chairs which had been stacked atop one another at the coffee shop fell over.

"The wind was strong and the rain was also very heavy, there were ice pieces everywhere - some even landed in the coffee shop," said the 53-year-old.

Although the Singapore Civil Defence Force said there were no reports of people who had been injured by trees, two visitors to the Singapore Zoo suffered pain in the ankle and abrasions when a falling tree branch hit them, a spokesman for Wildlife Reserves Singapore said.

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